This study will quantify the hypokalemic response to a graded infusion of epinephrine in adult family members who are definities affected or not affected. A large family (at least 20 living affected members) with hypokalemic periodic paralysis,is being studied. If there is a clearcut difference in the magnitude of response, young individuals (in their teens) will be tested to see whether the epinephrine challenge is useful as a diagnostic test.